Fluid valves exist in a wide variety of forms and sizes, serving a multitude of purposes, handling flowable materials including those ranging from light gas to heavy slurries and near-solids, and operable at various speeds under controls as diverse as simple binary (ON-OFF), proportional, direct-manual and remote-electrical. Those which are capable of responding quickly to govern even relatively large flows with precision, and with expenditure of little electrical power, are of special interest in certain industrial processing, such as the automatic regulation of gases in semiconductor and integrated-circuit manufacture. Mass flow controllers, for example, are widely used in semiconductor and integrated-circuit manufacturing to control the delivery of process gases, and the mass flow controllers include such valves.
U.S. Pat. No. 4,796,854 shows a proportional-control solenoid-actuated valve assembly, capable of governing relatively large volumes and rates of flow swiftly and accurately with expenditure of relatively little electrical power. The disclosed valve assembly includes a movable valve member positioned by an armature having a substantially frictionless spring suspension, the armature being under influence of a special force-counterbalancer in the form of a bellows proportioned and disposed to exert upon it, automatically, neutralizing forces which are substantially equal and opposite to unavoidable pressure-induced imbalances afflicting the valve member. The same pressures which tend to unbalance the valve member are impressed upon opposite sides of the bellows, one through an enabling bleed port, and resulting forces developed by the bellows over a defined area are exerted upon the armature mechanically in a counterbalancing sense.
Other examples of more refined valve assemblies can be found in the Type 1479 and Type 1640 mass flow controllers available from MKS Instruments, Inc. of Andover, Mass. (http://www.mksinst.com). As is known, a MFC is for controlling the flow rate of a gas from a source and can be used, for example, in the semiconductor manufacturing industry to precisely deliver a process vapor to a process chamber for making a semiconductor wafer. The MFC can be a temperature-based MFC or a pressure-based MFC, as well as other types of flow control devices. The MFC generally includes a flow path connected to an entering flow path of the valve assembly, a flow sensor assembly for sensing flow through the flow path, and a control device programmed to receive a predetermined desired flow rate from a user, receive an indication of flow from the flow sensor assembly, and determine an actual flow rate through the flow path. The control device is also programmed to instruct the valve assembly to increase flow, if the actual flow rate is less than the desired flow rate, and to decrease flow, if the actual flow rate is greater than the desired flow rate. The control device can comprise a computer processing unit (CPU) including at least a processor, memory and clock mounted on a circuit board. The control device operates in a feedback loop to maintain the desired flow at all times. When used with a proportional-control solenoid-actuated valve assembly, information on flow rate as a function of the valve assembly control current is preferably stored in the control device in order to quicken the response time of the MFC.
These existing designs, accordingly, provide excellent proportional-control solenoid-type valves which can swiftly and accurately govern even relatively large volumes and high rates of fluid flow using relatively low levels of electrical power, since the valves are aided by the force counterbalancing achieved through the use of the bellows-type coupling. These existing valve assemblies also provide sensitive and precise valving by way of the frictionless suspension of broad-area valve members and the counterbalancing of undesirable pressure-generated forces through a correlated pressure-responsive coupling. One drawback of solenoid valves, however, is that they are relatively expensive, have a low range, and are sensitive to vibrations.
What is still desired is a new and improved valve assembly. The valve assembly will preferably provide the benefits of previous valve assemblies, yet will be relatively inexpensive, have a wide dynamic range, and provide linear operating conditions (flow versus valve member position). The valve assembly will preferably also be capable of all metal construction so that the valve assembly can be used in a variety of gas flow applications.